Botulism of human infants is a recently identified syndrome whose widespread occurrence is now being recognized. This botulism differs from the classical food poisoning in that botulinum toxin is not ingested. Apparently Clostridium botulinum spores are accidentally swallowed; these are then able to germinate so that in vivo toxin production accompanies the ensuring vegetative multiplication in the digestive tract. The objectives of this research are to understand the susceptibility of infants and the refractoriness of adults to intraintestinal colonization by C. botulinum. Experimental studies are now possible with the demonstration that conventionally raised, 8-11 day old infant mice have botulinum toxin in their large intestine after they are given an intragastric challenge of botulinum spores. Spores of several C. botulinum types A, B and E culture strains will be tested to determine if the 50 percent infective dose of some is less than the 300 spores/mouse established for the one strain studied to date. Infected suckling mice do not develop overt botulism and human infant cases have had uneventful recoveries when released from hospital care at the time they are excreting toxin in their feces. Studies will be made to elicit botulism in infant mice whose gut motility has been slowed with drugs; the possible relationship between toxic response to quantity and location of toxin in the different levels of the digestive tract will be ascertained. Adult and infant gnotobiotic mice will be associated with autochthonous flora of the intestinal tract to determine the groups of bacteria which make the digestive tract susceptible or refractory to multiplication of C. botulinum.